1. Field of the Invention
The present invention relates to a catalyst used to selectively remove carbon monoxide (CO) in a hydrogen rich gas according to a water gas shift reaction, and a production method therefor.
2. Disclosure of the Prior Art
In recent years, proton-exchange membrane fuel cells having advantages of a low operation temperature, high power density, reductions in size and weight and an accelerated start-up time receive widespread attention as a fuel cell power generation system of the next generation, and are expected in applications to cars, compact electric generators, home cogeneration devices and so on. In the proton-exchange membrane fuel cells, a perfluorosulfonic acid based polymer film is used as a proton-conductive solid electrolyte, and can be operated at a temperature between 50xc2x0 C. to 100xc2x0 C.
However, since a hydrogen rich gas generated by a reaction between steam and a hydrocarbon fuel or an alcohol fuel such as methanol is used as a hydrogen source for the fuel-cell power generation system, there is a problem that the proton-exchange membrane fuel cells easily receive damages by the presence of impurities in the hydrogen rich gas. In particular, carbon monoxide (CO) in the hydrogen rich gas gives considerable damages to platinum used as electrode materials. When the CO concentration in the hydrogen rich gas exceeds a threshold value, the power generation capacity lowers.
To avoid the damages of platinum caused by carbon monoxide, it is proposed to set up a CO removing device for removing carbon monoxide in the hydrogen rich gas such that the CO concentration becomes about 1% or less, and a device for selective oxidation reaction of further reducing the CO concentration to 50 PPM or less.
By the way, the CO removing device uses a catalyst for selectively removing carbon monoxide in the hydrogen rich gas according to a water gas shift reaction. As this kind of catalyst, for example, Japanese Patent Gazette No. 3215680 discloses a catalyst for a water gas shift reaction, which is characterized in that platinum and rhenium are supported on a support of zirconia. There are advantages this catalyst shows a higher catalyst activity than a conventional copper-zinc catalyst, and a deterioration with time of the catalyst performance is relatively small.
However, there is a problem that the CO conversion of the catalyst according to the water gas shift reaction rapidly decreases under conditions of a reaction temperature of 250xc2x0 C. or less and a high space velocity, i.e., a large supply amount of the hydrogen rich gas. This means that a higher reaction temperature is needed to efficiently remove carbon monoxide in the hydrogen rich gas. In addition, since a relatively large amount of platinum must be supported on zirconia to obtain a desired catalyst performance, there is still plenty of room for improvement in cost/performance of the catalyst.
Therefore, a primary object of the present invention is to provide a catalyst for removing carbon monoxide in a hydrogen rich gas, which has the capability of providing an improved CO conversion at a relatively low reaction temperature between 200xc2x0 C. and 300xc2x0 C. and excellent cost/performance due to a reduction in amount of platinum used in the catalyst, while maintaining the advantages of a conventional catalyst characterized in that rhenium and platinum are supported on zirconia. That is, the catalyst of the present invention is characterized in that platinum and rhenium are supported on rutile titania.
It is preferred that an amount of supported platinum is in a range of 0.05 to 3% with respect to catalyst weight. In addition, it is preferred that an amount of supported rhenium is in a range of 0.01 to 10% with respect to catalyst weight.
It is also preferred that a weight ratio of an amount of supported platinum to an amount of supported rhenium is in a range of 3:1 to 1:1.
Another object of the present invention is to provide a preferred method of producing the above-described catalyst. That is, the method comprises a first step of supporting rhenium on rutile titania, and a second step of supporting platinum on the support after the first step. In this case, there is a great advantage that a CO conversion of the catalyst according to the water gas shift reaction is 60% or more when it is measured at a reaction temperature of 250xc2x0 C., with respect to a mixture gas obtained by mixing a hydrogen rich gas containing about 12% of carbon monoxide with water such that a mole ratio of H2O/CO is substantially equal to 4.3, in the case that an amount of the hydrogen rich gas treated per unit weight of supported platinum is in a range of 5000 to 5500 [cc/(minxc2x7g(Pt))].
These and still other objects and advantages of the present invention will become more apparent from the following detail description and preferred examples of the present invention, referring to the attached drawings.
The present disclosure relates to subject matters contained in Japanese Patent Application No. 2002-111232, which was filed on Apr. 12, 2002, the disclosure of which is expressly incorporated herein by reference in its entirety.